Treatment of corrosion in water systems is typically achieved by continuous application of various corrosion inhibitors in the water including, for example, phosphates, polymer, chromates, zinc, molybdates, nitrites, and combinations thereof. These inhibitors work by the principle of shifting the electrochemical corrosion potential of the corroding metal in the positive direction indicating the retardation of the anodic process (anodic control), or displacement in the negative direction indicating mainly retardation of the cathodic process (cathodic control). Corrosion inhibitors act on the cathode and/or anode of the corrosion cell.
A common and practical approach of corrosion protection is by changing the environment around the metal surfaces. Due to this reason, in conventional anti-corrosion treatment programs, continuous treatment of corrosion inhibitors is applied. The mechanism of corrosion inhibition was thought to require a continuous dose because of the equilibrium nature of the inhibitor film. If the maintenance dose of the inhibitor is interrupted, corrosion rates tend to increase quite quickly as the inhibitor film needs continuous replenishment. In the absence of any inhibitor, the film deteriorates rapidly. However, applying continuous inhibitors at high levels is associated with a high cost and can be particularly cost prohibitive in those instances in which the volume of water consumption is high. Continuous treatment methods also impact the effluent stream of the treated water systems and can result in toxicity issues, environmental concerns and/or additional costs associated with remedial treatment or enhanced handling of the effluent stream.
Historically, the use of Tin compounds as a corrosion inhibitor has been the subject of some experimentation in water systems like those described above. Stannous salts are known to inhibit corrosion but, unlike more conventional corrosion inhibitors, the mechanism by which the stannous salts inhibited corrosion was not well understood. Previous corrosion inhibition programs utilized the stannous salts in much the same manner as conventional corrosion inhibitors in which a maintenance dose of the stannous inhibitors were introduced into the aqueous systems to continuously maintain a minimum stannous concentration in order to be effective. Examples of such prior art methods may be found in, for example, U.S. Pat. No. 7,910,024 to Stapp et al. and U.S. Pat. Nos. 6,001,156 and 6,200,529 to Riggs, Jr., the contents of which are incorporated herein by reference, in their entireties.
Moreover, conventional corrosion inhibition practices with Tin compounds have not been able to effectively deal with the problem of maintaining an effective amount of Tin(II) in solution long enough to form a protective film on the surface of the corrosive metal without losing active form, Tin (II), due to bulk phase oxidation and precipitation to Tin (IV). These and other issues are addressed by the present disclosure. It is an object of this disclosure to provide methods for improved and effective use of Tin-based corrosion inhibitors by proposing a shot feed concept of applying corrosion inhibitor for a short period of time to form a stable and persistent film of Tin (IV) on the metal surface. This film of Tin (IV) is shown to last a few days without any more inhibitor present and the film is also shown to last much longer with a very small service dose of corrosion inhibitor.